So it does alter the steering geometry by increasing the distance between the top and botton swivel points on the stub axle. The difference appears to be very small and I'd be surprised if it were to make a difference at all.
We'll get too complicated if we try to discuss the cause of bump steer on here, but essentially you are trying to align the top and bottom chassis/wishbone pivot points along with the end of the steering rack so that the pick up points on the stub axle (top and bottom joints and track rod end) all move through the same arc.
Yes on a 7 where you are unable to move chassis pick up points, the only thing you can do is move the rack and this is by trial and error as it will vary from car to car depending on the ride height and amount of suspension travel.
If you are designing suspension from scratch the best way to eliminate bump steer is to have a short rack with long steering arms at the end so that it sweeps through a wide arc and thus introduces little lateral movement. Couple this to long wishbones with pivot points aligned and very limited suspension travel and Bob's your mothers brother. Look at F1 cars -they know what they're doing.
Paul Richards
Area Representative - L.A.D.S. (Lancashire and District Sevens)
LADS Website
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